Fingerprint readers may be seen in e.g. WO99/41696 and WO2005/124659.
In general, fingerprint readers are based on a technology which is not bendable, which brings about a problem when provided in bendable elements.
In a first aspect, the invention relates to a fingerprint reader comprising:                a fingerprint sensor adapted to output information relating to a fingerprint of a finger engaging a sensitive surface the sensor,        a stiff element comprising an indentation/cavity or through-hole,the sensor being positioned in the indentation/cavity/through-hole so that the sensitive surface is exposed to the surroundings.        
In the present context, a fingerprint reader is to be interpreted broadly as an element adapted to determine information relating to a fingerprint of a finger.
A fingerprint sensor is an element adapted to sense at least part of a fingerprint, and normally does so using a sensitive or sensing surface. A fingerprint sensor may be adapted to determine the whole (relevant part) fingerprint in one measurement, meaning that it has a sensitive surface of a sufficient size for the relevant part of the finger to contact it at the same time, or it may be adapted to have the finger swiped over the sensor in order to sense parts of the fingerprint sequentially.
The information output of the sensor may be any type of information from which information may be derived about the fingerprint. This may be 2D information describing the positions/shapes of ridges or valleys of the fingerprint or more complex and/or more compressed data. This differs widely from sensor to sensor.
In the present context, a stiff element is an element providing/supporting the sensor with a sufficient stiffness to not bend too much when exposed to a predetermined force. Naturally, this feature will differ from application to application, depending on how rugged the sensor has to be, but for use in e.g. a credit card, a stiffness is preferred of 100 N/mm2 or more, such as 150 N/mm2, preferably 200 N/mm2 or more, such as 250 N/mm2, preferably 300 N/mm2 or more, such as 350 N/mm2, preferably 400 N/mm2 or more.
In a preferred embodiment, the stiff element comprises a layer of a polymer, a metal, glass fibre/epoxy, such as a PCB, defining the overall stiffness of the stiff element and having a thickness of 0.2 mm or more, such as 0.4 mm or more, 0.5 mm or more, 1 mm or more.
Preferably, the indentation/cavity or through-hole has an extent along a main outer surface of the stiff element for the sensor to be positioned therein with the sensitive surface pointing away from the stiff element.
In a first embodiment:                the stiff element comprises one or more first electrical conductors,        the sensor comprises one or more second electrical conductors adapted to carry the output information, each of the second conductors being connected to a first conductor.        
In this embodiment, the stiff element may be a PCB, where the first electrical conductors are formed in the conductive layers of the PCB.
In one embodiment, such as the first embodiment, the stiff element further comprises one or more electrically conducting surface parts positioned adjacently to the sensitive surface of the sensor and being adapted to be contacted by a finger also contacting the sensor. These conducting surface parts may alternatively or additionally be positioned adjacent to an outer rim of the indentation/cavity/through-hole.
In this context, “adjacently” will mean that the finger will contact both the electrically conductive surface part(s) and the sensitive surface part of the sensor at the same time. Thus, normally, the sensitive surface part and the electrically conductive surface part(s) will be no more than 5 mm, such as 3 mm, preferable no more than 2 or 1 mm from each other.
In that embodiment, it is preferred that the reader further comprises means for providing a signal to the conductive surface part(s) where the sensor is adapted to provide the output information on the basis of the signal provided to the surface part(s).
Preferably, the so-called Active Capacitive Measurement is used, wherein an RF signal is input into the finger via the conductive surface(s) and sensitive elements of the sensor will sense the signal, like antennas, as the signal strength depends on the capacitance/resistive connection, so from the distance between the skin and the pixel.
Also, positioning the sensor and conductive surface(s) in a fixed position in relation to each other will enhance the detection and structure of the set-up.
In that or another embodiment, the reader further comprises a processing element comprising identity information, the processing element being adapted to:                receive the output information from the sensor,        compare the received information to the identity information and        determine a correspondence between the received information and the identity information.        
In this context, “correspondence” will relate to the actual type of information. What is important is that, from the information, it may be determined whether the finger print detected/sensed corresponds to that, information relating to which has been stored.
Thus, identity of a person may be determined on the basis of the determined fingerprint information and predetermined identity information, which may be stored in or in connection with the sensor.
In this respect, the positive identification of the person or the corresponding of the information may bring about the running of an application which is only available upon positive identification. This application may relate to the transmission of data as a part of a money transaction or the opening of a door/access to an area. Any application today handled by smart cards or identification tokens may be started in this manner.
A particularly interesting aspect relates to a credit card size card comprising a fingerprint sensor according to the first aspect of the invention.
A credit card size card is a card having a longest dimension of 15 cm or less, and a thickness of 3 mm or less. In fact, a size as that of standard credit cards is preferred. One definition of this type of card is the so-called ID-1 size card.
Such credit cards must be bendable, as is stated in the ISO/IEC 10373-1 standard, the card, subjected to a test load, must have a deformation between 35 and 13 mm and must return to no more than 1.5 mm from its flat condition within one minute after the load is removed.
This required bendability brings about a problem for the sensor. Thus, it is preferred that the sensor is stiffened, or the surroundings of the sensor are stiffened by the stiff element. In addition, it is desired to retain an overall required stiffness/bendability of the card, so that the extent of the stiff element, along the longest side of a rectangular card, is no more than 25%, such as no more than 20%. Thus, the remainder of the card may be allowed to bend, while the surroundings of the sensor are more stiff.
In this aspect, it is preferred that the card further comprises a processing element adapted to receive the output information from the sensor, wherein the stiff element further comprises one or more electrically conducting surface parts each connected to the processing element. Thus, the signal from the sensor may be provided to the processing element via the stiff element, which may be a PCB to which the processing element may be connected to also provide this element with a certain stiffness and protect it from excessive bending.
A final aspect of the invention relates to a method of operating the fingerprint reader according to the first aspect or a card according to the particularly interesting aspect, the method comprising:                a finger engaging a sensitive surface of the sensor,        the sensor outputting corresponding output information.        
Thus, the sensor is supported or stiffened by the stiff element both during operation and during inactive periods where the user may handle the reader in a more casual manner.
In one embodiment, the stiff element comprises one or more first electrical conductors, the method comprising conducting the output information to the first electrical conductor(s). Thus, the stiff element is used not only for stiffening but also for transporting signals away from the sensor.
In that or another embodiment, the engaging step comprises the finger additionally contacting one or more electrically conducting surface parts of the stiff element positioned adjacently to the sensitive surface of the sensor. Then, and in particular when the outputting step comprises providing a signal to the conductive surface part(s) and providing the output information on the basis of the signal provided to the surface part(s), a better fingerprint reading may be obtained.
Positioning the sensor in relation to the stiff element and using also the surface of the stiff element will bring about a more simple set-up while facilitating a good relationship between the relative positions of the two elements.
In another embodiment, the method further comprises the steps of:                comparing the output information to predetermined identity information and        determining a correspondence between the received information and the identity information.        
Thus, the identity of a person or the allowability of the person to use the e.g. card for e.g. transactions, access or the like may be determined, and a processing element of the card or the like may subsequently be used for handing additional operations which are allowable/run/started only when the correct fingerprint has been entered.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embdiments of the invention, are given by way of illustration only, since various changes and modifications within the spirt and scope of the invention will become apparent to those skilled in the art from this detailed description.